Early data in the literature suggests that total numbers of Epstein-Barr viral gemones increases in peripheral blood of organ transplant patients prior to diagnosis of post-transplant lymphoproliferative disorders (PTLD). This study would try to corraborate this data and further attempt to detect emerging EBV-infected clonal populations in peripheral blood of these patients. It is presumed that detection of increasing Epstein-Barr viral load and/or emerging clonal populations will define a group of patients who would benefit from decreased immunosuppressive therapy.